1. Field of the Invention
The present invention relates to an electrophotographic image-forming apparatus and a toner cartridge detachably attached to the electrophotographic image-forming apparatus.
2. Description of the Related Art
Japanese Patent Laid-Open No. 2002-72657 discloses a conventional image-forming apparatus that includes a toner cartridge with a toner-agitating rod. The toner-agitating rod has one end with a magnetic member and the other end coupled to a toner-agitating shaft. The apparatus has a top cover, which is pivotally coupled to a main body and has a sensor mechanism. The sensor mechanism has a permanent magnet that opposes the magnetic member. The sensor mechanism detects the rotation of the toner-agitating shaft. The toner-agitating rod performs sliding motion within a guide provided on the top cover and the sensor mechanism operates in cooperation with the sliding motion of the rod. The magnetic member at one end of the toner-agitating rod stays longer at the upper portion of the guide when a relatively small amount of toner remains in the toner cartridge, and shorter when a relatively large amount of toner remains in the toner cartridge. The sensor mechanism detects the difference in time and a controller checks the detection result to determine an amount of toner remaining in the toner cartridge.
With an electrophotographic image-forming apparatus, if a photoconductive drum remains in contact with a transport belt for a long period of time, chemical reaction takes place between these structural members, contaminating the surface of the photoconductive drum. In color printing, the image forming sections for four colors descend to their down-positions at which the photoconductive drums are in contact with the transport belt. In black only printing, the three color image-forming sections ascend to their up-positions at which the photoconductive drums are not in contact with the transport belt.
A sensor detects the movement of the image-forming section between its up-position and down-position to generate a binary detection signal.
With the aforementioned image-forming apparatus, because the sensor mechanism is located on the top cover which is pivotally coupled to the main body of the apparatus, the sensor mechanism cannot be accurately positioned relative to the toner cartridge. Thus, the toner remaining in the cartridge cannot be detected accurately.
The toner-agitating rod in the toner cartridge moves in the pile of toner and therefore, receives a large load. Additionally, because the toner-agitating rod also moves in the pile of toner, the toner tends to clog the guide. Clogging of the guide is an obstacle to the motion of the toner-agitating rod, causing errors in detecting a remaining amount of toner.
With the aforementioned color photographic printer, the image-forming sections are positioned at different heights relative to the transport belt for color printing and monochrome printing, thereby preventing contamination of the photoconductive drums. For this purpose, the motors for driving the image-forming sections are rotated in the reverse direction, and cam mechanisms and up-position and down-position sensors cooperate to change the heights of the image forming sections relative to the transport belt. However, each color image-forming section requires a corresponding sensor in order to switch the color image-forming section between the up-position and the down-position. In addition, the requirement of the circuits and control to detect the outputs of the sensors adds to the manufacturing costs.